Chemical Mechanical Polishing (CMP) is a process widely used in the manufacture of semiconductor devices. Layers and structures are deposited and formed on a semiconductor substrate by various processes. Usually, these formation processes result in a surface that is not planar, or certain features formed in the substrate being covered and needing to be exposed. CMP is a process by which material is removed from the surface of a substrate to make it more planar (sometimes this process is referred to as Chemical Mechanical Planarization) and to expose desireable features.
During the CMP process, a polishing pad is used to remove material from the substrate, which is the mechanical aspect of the process. The pad abrades the surface of the substrate, usually with the help of an abrasive composition applied to the pad. The abrasive composition may include components selected to enhance the removal process chemically, providing the chemical aspect of the process. Some variations additionally use electrochemical means to enhance the process further (Electrochemical Mechanical Planarization or Polishing). As material is removed from the substrate, it collects on the pad and builds up in the abrasive composition. Also, as the pad is used its abrasive quality diminishes due to wear. Buildup of polishing byproduct material, and wear on the polishing pad requires that the pad be conditioned to restore its polishing capability. New pads must also be conditioned before they can be beneficially used.
Pad conditioning generally involves scouring the pad with an abrasive article to remove material that may be fouling the abrasive surface of the pad and to restore roughness to the pad. A conditioning pad contacts the polishing pad, abrading material from the pad and cutting grooves and features into the surface of the pad to restore roughness.
It is a constant challenge in the semiconductor industry that devices formed on semiconductor substrates grow smaller and denser over time. As devices grow smaller, all processes involved in forming the devices are challenged to produce these devices reliably. CMP processes are no exception. The smaller devices are more delicate, the layers to be removed from the substrates are thinner, the layers beneath that need to be preserved are thinner, and the features to be exposed by polishing are smaller and more easily damaged. The tolerance for variation in all processes is less, and new methods are required to meet these tolerances.
FIG. 1 is a graph showing the result of a prior art conditioning process. For a given conditioning pad, the effectiveness of conditioning the pad declines as successive substrates are processed on the apparatus. Line 102 illustrates this tendency. As a result, the effectiveness of the pad in polishing substrates drifts over time, producing non-uniform results from substrate to substrate. It is desired that conditioning effectiveness be more uniform, as hypothetically illustrated by line 104, to remove this source of variation and improve process results.
Thus, there is a continuing need for a method and apparatus for conditioning a polishing pad that yields uniform pad performance over the life of the conditioning pad as successive polishing pads are conditioned.